VISCOSITY 197 



in the solution, and it must be our task to correlate the influence 

 of electrolytes on viscosity with corresponding variations of the 

 volume of the protein in solution. 



The question then arises, How can the same mass of protein 

 particles in solution change its relative volume under the influ- 

 ence of electrolytes? This is only possible if the relative volume 

 occupied by the protein in the solution is increased by water 

 shifting from solvent to solute. We, therefore, have to find out 

 whether or not a shifting of water from the solvent to the solute 

 is possible, so that the volume of the solvent is diminished and 

 that of the solute increased. It is generally assumed that the 

 mechanism for such a transfer of water from solvent to solute is 

 explained by Pauli's hydration theory which has been repeatedly 

 referred to in this volume. Pauli suggested that the ionized 

 molecule of protein is surrounded by a shell of water which is 

 lacking in the non-ionized molecule. When protein is ionized, 

 i.e., by the addition of acid or alkali to isoelectric protein, a shell 

 of water is formed around each individual protein ion. On this 

 basis we can understand why the viscosity of a solution of iso- 

 electric protein should increase with the addition of acid or 

 alkali. The work of Lorenz, Born, and others, however, casts a 

 doubt on the assumption of a general hydration of polyatomic 

 ions. There are still other facts which show that the mere 

 ionization and consequent hydration of the individual protein ions 

 cannot well be the cause of the influence of the pH on the relative 

 viscosity of gelatin solutions. 



Gelatin solutions show the characteristic influence of the pH 

 on their viscosity, as is demonstrated in Fig. 48. The viscosity 

 of gelatin solutions behaves qualitatively as we might expect on 

 the basis of Pauli's hydration theory. Yet, if hydration of the 

 individual protein ions were the cause of the variation of the 

 viscosity of gelatin solutions, a variation of the hydrogen ion 

 concentration should have a similar influence on the viscosity 

 of solutions of simple amino-acids, like glycocoll and alanine, to 

 that which it has on the viscosity of gelatin solutions. Five 

 per cent solutions of glycocoll and alanine were brought to differ- 

 ent pH, from 5.0 to 2.0 and below, by the addition of HC1. 

 Miss Brakeley found, in the writer's laboratory, that the variation 

 of the pH of 5 per cent solutions of these two amino-acids between 



